1. Field of the Disclosed Subject Matter
The disclosed subject matter relates generally to stretchy polymer drawstrings or drawtapes, processes of making the same and applications of the same. Particularly, the disclosed subject matter relates to multilayer stretchy drawstrings including at least a first layer of elastomeric polymer and second and third layers of thermoplastic polymer and processes of making the same where the drawstring is stretched beyond the deformation limit of the thermoplastic polymer layers and allowed to elastically recover.
2. Description of Related Art
In order to maintain sanitary conditions, plastic bags have been used to line waste receptacles in both institutional and commercial practice. The plastic liner bag prevents waste or other materials from contacting the receptacle, as well as providing a simple and easy way to empty the container.
Because of the large variety of container sizes, it is difficult to secure the bag to the container so that it will not slide down into the receptacle. Merely folding the top of the bag over the sides of the receptacle is not satisfactory, since the materials in the bag tend to pull the bag into the receptacle.
A variety of drawstring plastic bags have been developed and typical drawstring bags include a drawstring or drawtape in a hem at the mouth of the bag. Drawstrings in such typical drawstring bags can be manufactured to be very thin and therefore inexpensive. However, the drawstring in a typical bag is not elastic and must be pulled tight in order to secure the bag to a trash container or to close the bag after use. It is preferable to have an elastic drawstring that naturally contracts to secure the bag to a trash container.
Drawstring bags with elastic mouth features have been developed to enable a bag to be securely fitted to the upper portion of a trash container while not interfering with the intrinsic strength and operation of the drawstring. Such elastic drawstrings have been developed as either a single layer of elastomers, a single layer of blended copolymers, or laminates of one folded plastic layer and one elastic layer. These approaches require 50% to 200% thicker drawstrings than typical non-elastic polymer drawstrings and are more expensive to produce both due to material cost as well as machining costs.
Such conventional drawstring bags generally have been considered satisfactory for their intended purpose. Recently, however, it has been found that in the monolayer elastomeric drawstring approach, drawstrings either exhibit too high an elasticity without real strain hardening or are too stiff to be stretched at low strain to fit around a trash container. A better balance of mechanical properties has been achieved with laminates of one folded plastic layer and one elastic layer. However, the manufacturing process for such laminates is complex and it can be difficult to get satisfactory seal strength between the elastomeric layer and the folded plastic layer.
U.S. Pat. No. 4,509,570 describes a plastic bag which has an elastic loop positioned in the hem at the top of the bag. The elastic loop provides a means to hold the bag at the top of the receptacle as well as to close the bag when it is removed from the receptacle. The elastic loop is in a highly stretched state when the bag is open and closes the top of the bag automatically when removed from the receptacle. It is difficult and expensive to manufacture a bag with the elastic band in a highly stretched state. Further, a bag having the automatic closing feature of this patent can provide a safety hazard to a child who may inadvertently obtain one of the bags and place the bag over his head. A bag having a similar elastic top is found in French Patent No. 1,419,805.
In U.S. Pat. No. 4,747,701 a plastic liner bag is described which has an elastic band partially secured to the open top of the plastic bag. The plastic band is used to overlap the top of a receptacle to hold the bag in place on the receptacle. This band cannot be used as a drawstring to close the top of the bag when it is filled. French Patent No. 1,367,590 also describes a bag having an elastic top which does not act as a drawstring.
U.S. Pat. No. 5,691,034 (“the '034 patent”) describes non-tacky, microtextured, multilayer elastomeric laminates. The laminates include an elastomeric polymeric core layer, which provides elastomeric properties, and one or more polymeric skin layers that are capable of becoming microtextured. The '034 patent defines microtexture as the surface containing peak and valley irregularities or folds which are large enough to be perceived by the unaided human eye as causing increased opacity over the opacity of the laminate before microtexturing, and which irregularities are small enough to be perceived as smooth or soft to human skin. The desired microtexturing in the '034 patent provides lowered coefficient of friction and modulus, which results in a soft and silky feel. The microtexturing is created by stretching the laminate past the elastic limit of the skin layers. Due to the thin skin layers and the relatively thick elastomeric core layer, the skin layers buckle upon recovery to create a microtextured surface. The laminates of the '034 patent are useful in the garment area where the soft feel of the microtextured surface is desirable. The '034 patent in particular suggests use of the microtextured laminates as waistbands in diapers or as soft wipes. However, the microtextured laminates of the '034 patent are not suitable for use as drawstrings or drawtapes in a plastic bag due to the dominant elastomer content required to create the microtexturing as specified. The elastomer content of the '034 patent results in laminates that are overly elastic for use in drawstring plastic bags, as one cannot pick up a bag using a drawstring that is too elastic. Additionally, the microtextured skin of the '034 patent laminates is not desirable for sealing such a laminate to a plastic bag.
As evident from the related art, conventional elastic drawstring bags often require 50% to 200% thicker drawstrings than typical non-elastic polymer drawstrings and are more expensive to produce both due to material cost as well as machining costs. Certain conventional elastic laminates have desirably thin profiles, but are too stretchy or have textured surfaces that are not suitable for use in a drawstring bag.
Therefore, a need exists for a stretchy polymer drawstring that has elastic properties and matches the performance of prior polymer laminate drawstrings of one folded plastic layer and one elastic layer, while enjoying more efficient and economical manufacturing capability and having comparable gauge to traditional non-elastic monolayer drawstrings.